In a pixel structure of a liquid crystal display, it generally has to dispose a storage capacitor for storing a pixel data for a period of time till updated. The storage capacitor is usually formed by two metal layers. Since the two metal layers are not transparent, the arrangement of the storage capacitor is inevitable to sacrifice an aperture ratio of a display panel such that the aperture ratio is decreased.
FIG. 1 is top view of a conventional pixel structure. The pixel structure shown in FIG. 1 is a pixel structure of an in plane switching (IPS) structure. The pixel structure is formed by interlacing a gate line 111 and a data line 151. The pixel structure comprises a thin-film transistor structure 19, a pixel electrode 171, a common electrode 181, and a storage capacitor 10. The thin-film transistor structure 19 comprises a gate electrode 113, a source electrode 152, and a drain electrode 153. The gate electrode 113 of the thin-film transistor structure 19 is electrically connected to the gate line 111. The source electrode 152 is electrically connected to the data line 151. The pixel electrode 171 is electrically connected to the drain electrode 153 of the thin-film transistor structure 19 via a contact hole 161. The common electrode 181 is electrically connected to the common line 112 via another contact hole (not shown). The pixel electrode 171 and the common electrode 181 are located at the same layer, and this is the electrode arrangement of the IPS structure. The electric field formed therebetween can make liquid crystal molecules twisted.
The storage capacitor 10 comprises a bottom electrode 11 and a top electrode 15. The bottom electrode 11 and the top electrode 15 have an insulating layer (not shown) disposed therebetween. The bottom electrode 11 is formed by extending the common line 112 upward and downward. The top electrode 15 is extended from the drain electrode 153 to a region above the bottom electrode 11. The bottom electrode 11 and the top electrode 15 of the storage capacitor 10 both are opaque metal layers. As described above, the arrangement of the storage capacitor 10 will decrease the aperture ratio of the display panel.
In another aspect, it has to persist with a certain amount of capacitance of the storage capacitor when designing a pixel structure. If the storage capacitor is too small, it will cause a large feedthrough voltage such that a flicker may be occurred on a screen or the screen may be blinking. In the conventional pixel structure, increasing the storage capacitor is inevitable to increase the areas of the top electrode and the bottom electrode. This will reduce the aperture ratio and affect the quality of the display panel as well.
Therefore, how to develop a pixel structure and persist with a certain amount of capacitance of the storage capacitor without decreasing the aperture ratio or further, improving the aperture ratio, is an importance issue in this industrial field.